Method for desiccating and defoliating plants with arsinic acid derivatives



United States Patent 3,497,341 METHOD FOR DESICCATING AND DEFOLIATING PLANTS WITH ARSINIC ACID DERIVATIVES Max Eugene Chiddix, Easton, Pa., assiguor to GAF Corporation, a corporation of Delaware No Drawing. Filed May 19, 1966, Ser. No. 551,206 Int. Cl. A01n 9/00; C07f 9/70 US. CI. 71-70 3 Claims ABSTRACT OF THE DISCLOSURE Plants are dessicated and defoliated by treating the foliage with an arsinic acid compound having the general formula:

wherein R represents a radical selected from the group consisting of n-propyl and n-butyl radicals, wherein R represents a member selected from the group consisting of hydrogen, methyl and ethyl radicals and wherein M represents a member selected from the group consisting of hydrogen, an alkali metal, an alkaline earth metal, ammonium and amino salt-forming groups.

This invention relates to chemical treatment of vegetation to obtain leaf desiccation and defoliation. More particularly, it pertains to the desiccation and/or defoliation of vegetation by means of a selected arsinic compound.

The rarity of chemicals with defoliant action, or with an appropriate type of leaf desiccation, is well recognized in agricultural science. Although many chemicals are known to have herbicidal properties, few have been found which are useful as defoliants. Experience has shown that a chemical which is herbicidal in its action on a particular plant is not usually a defoliant for the same plant. However, a chemical which is a defoliant may also be a herbicide, if used in amounts excessive for defoliation.

Development of successful defoliants has been a slow process. Prior to 1948 calcium cyanamide was the only commercially successful and available defoliant. Since 1948 only about a dozen new defoliants have been found and developed. These include, for example, monosodium cyanamide, ammonium thiocyanate, potassium cyanate, sodium chlorate-sodium pentaborate, sodium chloratemagnesium chloride and 3,6-endoxohexahydrophthalic acid and its derivatives (US. 2,576,080, 2,576,081, and 2,576,082).

Arsenic compounds have found wide use as herbicides. Acid-arsenical sprays have been used for several decades to treat and kill many thousands of acres of morningglory, Russian knapweed, alkali mallow, and other perennial weeds in California and other western states. The recommended spray (see, for example Weed Control by Robbins, Crafts and Raynor, McGraw-Hill Book Company, 1942, p. 219) must contain at least one-half percent arsenic trioxide by weight and percent sulfuric acid. Lead arsenate has been used at the rate of 20 to 25 lbs. per 1000 sq. feet to control crabgrass. Ibid. p. 403. Arsenic pentoxide which forms arsenic acid in aqueous solution, has been used in the proprietary herbicide Pentox for killing weeds. Arsenic trichloride, formed by refluxing arsenic trioxide with concentrated hydrochloric acid, forms the poisonous principle in another proprietary herbicide, sold under the name K.M.G. Another trivalent arsenic compound, sodium arsenite, is the principal constituent of many other commercial Weed killers. The trivalent form of arsenic has been used more commonly than the pentavalent form because of the greater toxicity of the trivalent form. When applied to cotton plants,

sodium arsenite is known to kill and desiccate the plants.

I have now unexpectedly found that the leaf desiccation and defoliation of vegetation can be carried out with good commercial success and at a high rate of eifectiveness by using novel 2-hydroxy alkyl arsinic acid herbicidal compounds having the general formula:

wherein R represents an n-propyl or n-butyl radical, wherein R represents hydrogen or an alkyl radical and wherein M represents hydrogen or a salt-forming group.

More particularly, my invention pertains to the use of arsinic acid derivatives of 2-hydroxyl alkyl arsinic acid compounds having the general formula:

wherein R represents a member selected from the group consisting of n-propyl and n-butyl radicals, wherein R represents a member selected from the group consisting of hydrogen, methyl, ethyl, propyl and butyl radicals and wherein M represents a member selected fro-m the group consisting of hydrogen, an alkali metal, such as sodium, potassium, etc., an alkaline earth metal such as magnesium, calcium, barium, etc., an ammonium ion (NH and an amine salt such as a moiety from an amine such as methylamine, trimethylamine, triethylamine, ethanolamine, dibutylamine, ethylene diamine, morpholine, pyridine and the like.

The arsinic acid compounds of the instant invention may be prepared by reacting various arsenite compounds with oxides to form the arsinic salt which may be readily acidified to produce the corresponding acid as illustrated by the following reaction:

I CHZCHOHR CH2CHOH R wherein R is n-propyl or n-butyl and R may represent hydrogen or lower alkyl.

The intermediate n-propyl and n-butyl starting materials used in the preparation of the arsinic compounds of this invention may be prepared according to the following known reactions:

(2) As(ONa);,i-RX-- RAsO(ONa) (3) RAsO(ONa) +HCl+SO RAsCl (4) RAsCl +NaOI-l- RAs(ONa) 2 wherein RX may represent a n-propylhalide or n-butylhalide, such as n-propyl bromide or n-butyl bromide. Said reactions may be found more fully described in J. Am. Chem. Soc. 44, pages 805 and 1356 (1922).

It is obvious from reaction 1, dipicted above, that an alkali metal salt of the arsinic acid is formed first and that the free acid can be obtained by acidification. Other salts, such as alkaline earth metal salts, the ammonium salt, an amine salt or other alkali metal salts may be prepared by neutralizing the free acid with the corresponding base. This does not depart from the scope of the instant invention, since the salt is merely a matter of choice.

As examples of the various alkali metal alkylarsenite starting materials there may be mentioned sodium n-propylarsenite, sodium n-butylarsenite, potassium n-propylarsenite, potassium n-butylarsenite and the like.

Examples of Various bases which may be used to neutralize the arsinic acids are as follows: calcium hydroxide, calcium carbonate, magnesium hydroxide, barium hydroxide, lithium hydroxide, ammonium hydroxide, trimethylamine, triethylamine, methylamine, dimethyla mine, ethanolamine, diethanolamine, triethanolamine, ethylene diamine, morpholine, piperidine, pyridine, imidazoline, and quinoline.

By vegetation coming within the purview of this invention, we mean any plant life, particularly weeds, deciduous trees, vines, broadleaf plants, cereals, cotton, beans and peas. Specific test plants include Black Valentine bean, Heavenly Blue morning-glory, Scarlet Globe radish, Lincoln soybean and two cereal species, Clinton oats and rice, PI. 8970. The arsinic acid compounds may be applied to the foliage in their free acid form or in their salt form. In a living plant, because of the effect of buffer salts, the arsinic acid undoubtedly is converted to a salt during translocation.

The spraying or dusting of vegetation may be carried out by any known means, for example, by means of ground spraying or by airborne spraying equipment. While spraying and dusting is best done with airborne equipment, from the standpoint of efiiciency, other forms of spraying equipment may be used if the usual precautions well known in the art for handling poisonous materials are taken. Equipment should be thoroughly cleaned before use to remove any chemicals which could react with the arsinic acid compound to reduce its desiccating and defoliating activity. After use, the equipment should be cleaned to remove traces of arsinic acid which might contaminate other sprays used from the same equipment. Spraying is usually done under favorable conditions of sunlight, moisture, humidity and other factors. However, these factors have not been found to be critical in the successful practice of our invention.

In the practice of my invention for leaf desiccation and/or defoliation a solution of the arsinic acid compound is sprayed on the vegetation at a conventional herbicidal concentration. For example, an aqueous, an alcoholic or an acetone solution of the arsinic acid compound or one of its salts may be used in which the arsinic acid compound is present in amounts from about 1% to 50% by weight of the solution. The rate of application may vary from anywhere between about 0.1 pound to about pounds per acre. Especially good results have been obtained by application rates equivalent to about 0.1 pound and 1 pound per acre of the arsinic acid.

Customary formulating techniques may be used in preparing the arsinic acid compound solution to make it more eflicient in covering and penetrating the foliage of the plant to which it is applied. For example, a small amount of surface active agent, up to about 2% by weight of solution, may be added to an aqueous solution of the arsinic acid to increase its wetting and spreading ability on the leaves on which it is sprayed. Examples of suitable surface active agents include the alkyl aryl sulfonates, the alkyl polyglycol ethers, the alkylaryl polyglycol ethers, the alkyl sulfates and the sulfosuccinic esters. Typical agents are Igepal CO 630, Tween and EXAMPLE I Z-hydroxyethyl n-butyl arsinic acid Twelve grams (0.27 mole) of ethylene oxide were reacted with a solution of 51 grams (0.25 mole) n-butyldichloroarsine in ml. of 10 N sodium hydroxide solution. Acidification and concentration of the reaction solution followed by an ether extraction of the final concentrate resulted in the isolation of a slightly viscous ether solution. Removal of the ether left a very viscous residue which when dissolved in a minimum amount of methanol and diluted with ether yielded 15 grams of a white tacky solid. Concentration of the alcohol ether filtrate yielded 19 grams of a yellow, viscous oily product. Titration showed it to contain 89% of the desired arsinic acid.

This Z-hydroxyethyl n-butyl arsinic acid was soluble in water, alcohol and acetone and had a herbicidal activity rating. of 21, when evaluated as in Example II. It may be represented by the formula:

Similar results were obtained by replacing n-butyldichloroarsine with n-propyl-dichloroarsine and by substituting such oxides as 1,2-propylene oxide, 1,2-butylene oxide and 1,2-hexylene oxide for ethylene oxide.

EXAMPLE II Test procedure In a spray cabinet of Plexiglas having a bottom area of three square feet were placed pots containing plants of broadleaf species, i.e., Black Valentine bean, Heavenly Blue morning-glory, Scarlet Globe radish and Lincoln soybean, along with cereal species, i.e. Clinton oats and rice, P1. 8970. A spray solution was made up by dissolving 34 mg. of the test compound in 12.5 ml. of acetone containing 0.5% Tween 20. Seven days after planting, 12 ml. of the spray solution were vertically directed evenly over the three square feet of area and on to the potted seedlings at a spray rate equivalent to 1 pound per acre. The spray was applied to twelve pots simultaneously (two pots of each species). Visual observations were then made of the plants. Said observations were made at intervals of 2 days, 5 days and 10 to 14 days after treatment.

The various test compounds were given a rating of from 1 to 4 with regard to their herbicidal activity on each plant and cereal species tested. A rating of 1 indicates no discernable herbicidal activity. A rating of 2 indicates a slight, but not marked herbicidal effect. A rating of 3 indicates moderate or considerable injury to plant tissues. A rating of 4 indicates marked herbicidal activity characterized by killing or severe necrosis, defoliation, or other effects leading to death. The maximum rating for one species at one rate over all observed effects is 4. Thus, the highest rating for one rate of application on all the plant species tested is 24 (a total of 4 for each of the six plants species rated). Conversely, a rating of 6 indicates no visible elfect. Those compounds which receive a rating of 10 or above are fairly active; a rating of 12 to 17 is indicative of good activity, while a rating of 18 to 24 is evidence of very high activity.

The instant Z-hydroxyethyl n-butyl arsinic acid of Example I exhibited a herbicidal activity rating of 21 in this test at the 1 pound/acre application rate. It caused complete defoliation of the leaves of the Black Valentine beans.

Similar results were obtained with 2-hydroxyethyl npropyl arsinic acid, 2-hydroxypropyl n-butyl arsinic acid, 2-hydroxypropyl n-propyl arsinic acid, 2-hydroxybutyl npropyl arsinic acid and Z-hydroxybutyl n-butyl arsinic acid.

Various modifications and variations of this invention will be obvious to a worker skilled in the art and it is understood that such modifications and variations are to be included within the purview of this application and the spirit and scope of the appended claims.

I claim:

1. The method of desiccating and defoliating plants which comprises applying to the foliage an arsinic acid compound having the general formula:

wherein R represents a radical selected from the group consisting of n-propyl and n-butyl radicals, wherein R represents a member selected from the group consisting of hydrogen, methyl and ethyl radicals and wherein M represents a member selected from the group consisting of hydrogen, an alkali metal, an alkaline earth metal, ammonium and methylamino, trimethylarnino, triethylamino, ethanolamino, dibutylamino, ethylenediamino, morpholino, and pyridino groups at a rate sufiicient to cause defoliation of said plants and equivalent to from about 0.1 pound to 10 pounds of arsinic acid per acre of plants.

2. The method according to claim 1, wherein R re- 6 presents a n-butyl radical, R represents hydrogen and M represents hydrogen.

3. The method according to claim 1, wherein R represents a n-propyl radical, R represents hydrogen and M represents hydrogen.

References Cited UNITED STATES PATENTS 2,999,745 9/1961 Bloom 71-70 3,130,035 4/1964 Culver 71-69 3,378,364 4/1968 Neuville et a1 717O FOREIGN PATENTS 16,500 8/1963 Japan. 13,778 7/1964 Japan.

US. Cl. X.R. 

